Graphene is a two-dimensional (2D) carbon nanomaterial in which the arrangement of carbon atoms is identical to that in a single atomic layer of graphite, and generally refers to a 2D carbon layered structure stacked with less than 10 carbon atom layers. Since the number of layers of graphene has direct impact on the distribution of the electron cloud thereof, graphenes with various number of layers have different optical and electric performances, and the controlled synthesis of graphenes with various number of layers is beneficial in practical applications.
Novoselov et al. (K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, Y. Zhang, S. V. Dubonos, I. V. Grigorieva and A. A. Firsov, Electric field effect in atomically thin carbon films, Science, 2004, 306: 666-669) employed a mechanical peeling method to peel single-layer and multi-layer graphene thin films from highly oriented pyrolytic graphene and observe them, but such preparation method is difficult to control and scale up; Kim et al. (K. S. Kim, Y. Zhao, H. Jang, S. Y. Lee, J. M. Kim, K. S. Kim, J.-H. Ahn, P. Kim, J.-Y. Choi and B. H. Hong, Large-scale pattern growth of graphene films for stretchable transparent electrodes, Nature, 2009, 457: 706-710) utilized a chemical vapor deposition method to deposit various number of layers of graphene on a nickle substrate using methane as the carbon source, but such method used a gaseous carbon source which might cause safety issues during storage and in the process of reaction and could not produce graphene in large scale. Zhang et al. (W. Zhang, J. Cui, C. Tao, Y. Wu, Z. Li, L. Ma, Y. Wen and G. Li, A Strategy for producing pure single-layer graphene sheets based on a confined self-assembly approach, Angew. Chem. Int. Ed., 2009, 48: 5864-5868) designed and synthesized a novel amphiphilic molecule having a polymerisable pyrrole group and used it as a structure inducer and a carbon source to prepare a mesoporous silica with a layered structure, and to prepare a single-layered graphene by in situ polymerization of the preorganized pyrrole groups in the mesopores and carbonization using the 2D reaction microcavity formed by the silica, but this method has a high requirement for the amphiphilic molecule which needs specialized design and synthesis, and the 2D template formed by the amphiphicle molecule was poorly stable and may fail in controlled synthesis.